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He believed automatic engineering controls could have prevented the incident, which killed Cindy Low, Kate Goodchild, her brother Luke Dorsett and his partner Roozi Araghi after a water pump malfunction.

"I was stunned that they continued to use administrative controls. You need to move on to engineering controls. Either that or do not use the ride," he said.

Mr Stewart said the risk of the conveyor belt continuing to drive after a raft collision was "so high" it needed engineering controls to prevent it happening.

He identified dozens more serious safety concerns during his inspection.

He said the ride was "quite deteriorated" due to corrosion, with parts of the infrastructure propped up with "bits of timber".

In his report, Mr Stewart said the causes of the accident included the reliance on administrative controls, the limitations of emergency controls systems and procedures, monitoring and prevention of rafts collision in the unloading area, water level monitoring and the gap at the end of the conveyor.

Previously, a safety report found the Thunder River Rapids ride was unsafe and there had been "little learning" from previous incidents.